Apparatus for forming rocket propellant grains



Dec. 31 1968 R. G. GUENTER 3,418,686

APPARATUS FOR FORMING ROCKET PROPELLANT- GRAINS ori inal Filed July 16,1965 INVENTOR/ 2126mm 6. Guam fer W 544,! ATTORNEW- 3,418,686 APPARATUSFOR FORMING ROCKET PROPELLANT GRAINS Richard G. Guenter, Wilmington,Del., assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Army Original application July 16,1965, Ser. No. 472,742, now Patent No. 3,390,210, dated June 25, 1968.Divided and this application Jan. 23, 1967, Ser. No. 622,379

3 Uaims. (Cl. 18-12) ABSTRACT OF THE DISCLOSURE A large grain propellantforming device having reduced, outwardly tapered and unreduced or diesegments. A disc shaped axially moveable ram is positioned in thereduced segment, and is utilized to extrude the propellant through amultiplicity of orifices positioned adjacent the outwardly taperedsegment. The movement of the extruded material is opposed or retarded bya disc shaped consolidation ram positioned in the die segment whichslides loosely on a stake. The retarding of the movement of the materialresults in a product having a large propellant grain while at the sametime relieving the stresses and strains generated by the extrusion.

This is a division of application Ser. No. 472,742, filed July 16, 1965,now Patent No. 3,390,210.

This invention relates to an apparatus for the extrusion of solid rocketpropellants.

The product of this invention has various uses, but may be employed toparticular advantage for purposes requiring large and complex shapes, asfor example, for the propellant charge in a jet propulsion rocket motor.

Whereas solid propellant charges, of formulation designated compositeand double-base, can and are made by processes termed casting, by farthe greatest quantity have been produced by the solventless extrusion ofdouble-base formulation, and the majority of the installed manufacturingfacilities in this country and elsewhere is of the latter type. Thisprocess comprises the mixing of the ingredients, usually in a watersuspension, followed by removal of the excess water such as bycentrifuging and hot air drying, then subsequent colloiding of thematerial on heated revolving rolls to form leathery sheets of propellant0.1 in. thick. These sheets are convolute wound into rolls, and in thisform inserted into a press, from which the propellant is forced, underhigh pressure, through a forming die. This die has a diminishingcross-sectional area, or approach section, followed by a length ofuniform cross-section and, if the final product so requires, has one ormore pins or stakes, that produce suitable perforations axially throughthe extruded product. Issuing from the press therefore, is aconsolidated propellant strand of uniform cross-section but considerablysmaller than before extrusion. The step of extrusion introduces stresseswhich must be relieved by high temperature annealing in order to fullystabilize the strain created. Also, the dynamic formation reflects thepresence of irreducible batch to batch variation in the chemical andphysical variations of ingredients, variations in all previousprocessing stages, and variations in the extrusion conditions, to adegree that the cross-section dimensions of the extruded grains varysufiiciently as to require subsequent machining to avoid excessivevariation of ballistic properties among a quantity of rockets loadedwith propellant charges made by the solventless extrusion process.

In the consolidation of the roll charge into a homogeneous strand, it iswell understood by the industry that the individual strips comprisingthe roll are welded nited States Patent 0 3,418,686 Patented Dec. 31,1968 ice together in the approach section of die by pressure and dynamicflow, coupled with a continuing reduction in cross-sectional area in theapproach section of the die. The minimum percentage reduction incross-sectional area necessary for consolidation varies with propellantcomposition and extrustion temperature, but is generally conceded to beabout 300%. Thus a standard press, having a basket 16 in. in diameter,can produce as a solid strand product not larger than 9 in. in diameter.Thus, the solventless extrustion process can produce only a smalldiameter product, only an axially symmetrical product, only a producthaving undesired internal stresses and a product that requires machiningto eliminate variations in cross-sectional dimensions.

It is therefore, the object of this inventon to eliminate the aboverestrictions by enlarging the die so that it contains the entirefinished charge an accomplishing the consolidation of the charge throughthe combination of a multiplicity of small orifices located at theentrance to the die and a retarding force that is asserted immediatelydownstream of said orifices.

In the drawing:

FIGURE 1 of the drawing is a diagrammatical illustration of theapparatus employed in carrying out the process of this invention;

FIGURE 2 is an enlarged cross-section of the stake,

taken on the 22 line of FIGURE 1.

In the drawing, the press basket 10 is filled with sheets of propellant11 which are extruded through partition 12 having a multiplicity oforifices 12a by the extrustion ram 13 which is powered through a shaft14. The extruded material passes into a guide chamber 15 of greaterdiameter and/or greater cross-sectional area. The movement of theextruded material is opposed or retarded by a consolidation ram 16 whichmaintains a friction tight fit at the perimeter and slides loosely on atapered stake 17 held in a centered position in the die 18 by a cap 19.The ram 16 supplies the initial retarding force necessary to push theextruded material against the expanding walls 20, so that instead ofmaking a propellant grain smaller than the press basket as is the usualcustom, is the means that permits a much larger grain to be formed inthe die. This retarding force also performs the additional function ofretaining the expanded material in the guide chamber long enough torelieve the strains in the material caused by extrustion. The ram 16supplies the retarding force when starting the operation, however oncethe ram is moved to the end of the die 18 and removed, the retardingforce is supplied by the friction in the guide chamber 15 of the solidmass of 21 against the walls 20. This friction continues to supply theretarding force necessary in succeeding operations and this forcecontinues to perform the dual function of consolidating the extrudedmaterial so that it is possible to make a considerably larger grain thanthe receptacle from which the material is extruded and at the same timewhile performing the consolidation function retaining the expandedmaterial a sufiicient period to relieve stresses and strains built up bythe extrustion. When the die 18 is filled With material, the die whichcontains a heating means (not shown) anneals the grain and the stake 17is withdrawn by means of the cap 19. The stake 17 is tapered in adirection opposite to the flow of material and has longitudinalprojections 22 tapered in direction opposite to the stake and taperedaxially towards the center which govern the interior shape of the grainand which may be varied by changing the shape of the stake so that manygeometrical configurations may be left in the interior of the graindepending upon the burning characteristics desired for any particulargrain. Thereafter the cured grain may be removed from the die and theprocess continues without the ram 16 used in the initial operation byreason of the friction generated, by the movement of the mass 21 of theextruded material against the expanding Walls 20 of the guide chamber15, supplying the retarding force necessary to produce a better and muchlarger grain.

The retarding force so essential to the operation of this invention wasobserved in the normal operation of extruding small diameter grains andappeared to occur possibly one in a million extrusions and changes weremade to prevent a recurrence of this occasional action. This observationrevealed that the product occasionally touched and adhered to anonfunctional, larger diameter metal sleeve and that the mass enlargedto fill the larger sleeve even though no back pressure was exerted.Thus, it is concluded that the powder to metal friction aloneaccomplishes the enlargement.

In the adaptation of this concept in actual practice, tests were foundto be completely satisfactory, however, the first few inches of theproduct were not consolidated and had to be cut-off. Therefore, to avoidwaste on the initial run, a plywood disk or ram was utilized and sizedso that it was a friction fit with the inside diameter of the mold and avery loose fit around the tapered stake, with a clearance of one to twoinches, which further demonstrates that substantial back pressure is notrequired. The ram Was not used after the initial extrusion, the firstcharge being cut free from the press basket in the area facing the ram16 leaving a heel of consolidated extruded powder that acts as theconsolidation ram for each succeeding extrusion.

One of the advantages of this process is that the pressure in the moldis extremely low and the mold need be only sufficiently rigid to insuredesired dimensional tolerances. Therefore equipment of nominal capitalinvestment may be used to replace expensive equipment limited to aproduct of small diameter, for example nine to ten inches and at thesame time produce a much larger more desirable product that may beaxially unsymmetrical or con tain other desired geometricalconfigurations within the grain.

What is claimed is:

1. An apparatus for forming a large grain propellant, comprising acylindrical press basket open at both ends containing sheets ofpropellant, a partition placed inside one end of the press basketcontaining a multiplicity of extrustion orifices, said partition soplaced as to provide a portion of the press basket of samecross-sectional area for movement of extruded material immediately afterpassage through said orifices, an extrustion ram in the other end of thepress basket for forcing the propellant through said orifices and theremainder of the press basket, a guide chamber with expanding walls toprovide a larger cross-section than the press basket, 2. consolidationram formed by the extruded material within the guide chamber madeoperational by the friction of the extruded material against theexpanding Walls, a die of greater cross-sectional area than the pressbasket connected to the guide chamber, a stake tapered in a directionopposite to the flow of material, having longitudinal projectionstapered in a direction opposite to the stake, said longitudinalprojections tapered radially towards the center and said stake attachedto a cap for the purpose of centering the stake in the die for theproduction of a rocket propellant charge larger in cross-sectional areathan the press basket and containing interior configurations regulatedby the shape of the stake.

2. An apparatus for forming a large grain propellant comprising:

a cylindrical press basket containing sheets of propellant having amultiplicity of small orifices at one end for extrusion of propellant,

means for extruding propellant from said press basket orifices toconsolidate the material,

a guide chamber attached to extrusion end of the press basket havingwalls tapering outwardly to force an increase in the cross section ofthe ex truded material,

said tapered walls producing a retarding force by reason of the frictionbetween the walls and the moving extruded material and a die attached tothe widest portion of the guide chamber to receive the extruded materialand form a propellant grain of substantially larger cross section thanthe press basket by reason of the delay caused by the retarding force inthe guide chamber.

3. An apparatus for forming a large grain propellant comprising meansfor extruding propellant material from a press basket through amultiplicity of small orifices for consolidation of extruded material, aguide chamber having outwardly tapered metal walls for receiving theextruded material, a die having non-tapered walls connecting with saidoutwardly tapered walls, a consolidation means positioned in said diechamber to provide an initial retarding force which directs the extrudedmaterial against the outwardly tapered walls thereby forming a betterand larger propellant grain, while at the same time relieving thestresses and strains generated by the extru- References Cited UNITEDSTATES PATENTS 2,332,829 10/1943 Parsons et al. 18-12 2,926,386 3/ 1960Hutchinson 2643 2,952,876 9/ 1960 Miles.

3,155,749 11/1964 Rossen et al. 264-3 3,252,369 5/1966 Bartley et al.264-3 CARL D. QUARFORTH, Primary Examiner.

M. I. MCGREAL, Assistant Examiner.

US. Cl. XJR. 18-3 0; 264-3

